you do it independently of the iron sights. some eotechs are already zeroed for 100yards give or take a few inches in either direction. Try it at 100 yards, if on target just make minor adjustments, 1MOA is 1/2 inch at 100 yards, if its really off at 100, set up your target at 25 yards, and zero that for about 1/4 to 1/2 below bullseye and it should be pretty close when shot at 100 yards. hope this helps you. If you have any more questions feel free to message me. Happy Hunting

1 moa is actually just slightly over an inch at 100 yds (1.047) but an inch is close enough. I think what upinflames means is that each click of adjustment on the eotech is 1/2 moa or 1/2" at 100 yards.